DNA sequencing of historical type specimens and recent collections reveals the identity of Hawaiian Porolithon (Corallinales, Rhodophyta) species.

The coralline red algal flora of the Hawaiian archipelago has been little studied. To date, only the smooth, crustose species Porolithon onkodes and the branched species, P. gardineri have been reported, both identifications based on morphology alone. More recent DNA studies in P. onkodes and other red algae have revealed that morphological-based species identification is highly error-prone and frequently misses the presence of cryptic species. We sequenced two plastid encoded loci (rbcL and psbA) from 18 field-collected samples from 4 sites on the North Shore of Oahu and determined the phylogenetic placement of these relative to other Porolithon sequences, including type specimens of named entities. None of the samples matched either P. onkodes or P. gardineri. Instead, we find 3 smooth, crustose Porolithon species apparently new to science, and not closely related to each other, based on the extent of sequence divergence at these two loci. The branched specimens in our collection closely match P. sandvicense, a name formerly subsumed within P. onkodes but which appears to be distinct, and whose type locality is Hawaii. The sister to each of these species in our phylogenetic analysis is not currently known to be present in Hawaii. We also do not see a clear division between smooth, crustose and branched morphologies in our phylogenetic analysis, suggesting that this distinction, widely used in the historical literature, may be of limited infrageneric taxonomic value. Our results suggest that many cryptic species in this group remain to be discovered in the Hawaiian archipelago and, by extension, the Pacific Basin.